A 54-year-old male patient underwent upper gastrointestinal endoscopy, which revealed a 25-mm brown region in the angular section of the greater curvature of the stomach. The region was histologically determined to be gastric mucosa with an accumulation of histiocytes containing eosinophilic substances in the cytoplasm and chronic inflammatory cell infiltration. Histiocytes were immunohistologically positive for CD68, IgG, and κ. Based on these findings, the patient was diagnosed with gastric crystal-storing histiocytosis comprised of histiocytes phagocytosing IgG-κ-type immunoglobulin. This is a rare disease of which there have been no previous reports that included long-term follow-up. Here, we report the case with a literature review.